In Japanese Unexamined Patent Application Publication No. 2002-232035, a mirror reflection layer is provided inside a fixed magnetic layer forming a spin valve thin film element. In order to obtain a mirror reflection effect, an NOL (Nano-Oxide Layer) is provided. “Ta 3 nm/NiFeCr 2 nm/CoFe 1.5 nm/NiFeCr 1 nm/PtMn 10 nm/CoFe 0.5 nm/NOL/CoFe 2 nm/Cu 2.3 nm/CoFeNi 2 nm/Cu 1 nm/TaO 1 nm . . . ” is described, and the fixed magnetic layer has a three-layered structure composed of a CoFe layer 0.5 nm thick, an NOL, and a CoFe layer 2 nm thick provided in that order.
In addition, a method for manufacturing an NOL is described where the NOL is to be formed by oxidation of a surface of a CoFe layer forming the fixed magnetic layer using plasma oxidation or the like.
An object is to obtain a preferable bias point and a high rate of change in resistance.
In Japanese Unexamined Patent Application Publication No. 2002-117508, a ferromagnetic fixed magnetic layer 15 having a laminated structure is disclosed, for example, in FIG. 3 thereof, and the ferromagnetic fixed magnetic layer 15 has a synthetic ferrimagnetic pinned structure formed of ferromagnetic films with an antiparallel coupling layer 150 made of Ru or the like interposed therebetween. The magnetizations of the ferromagnetic films formed on the top and the bottom of the antiparallel coupling layer 150 are fixed antiparallel with each other. After various experiments which will be described later were carried out by the inventors of the present invention, it was found that the rate (ΔR/R) of change in resistance is not effectively increased in a spin valve thin film element having the structure described in Japanese Unexamined Patent Application Publication No. 2002-232035.
That is, although the three-layered structure composed of the CoFe layer, the NOL, and the CoFe layer was used as the fixed magnetic layer, according to the experiments which will be described later, compared to the structure in which the NOL was not provided for the fixed magnetic layer, the rate (ΔR/R) of change in resistance was not so much improved as expected.
In addition, as another embodiment, when an experiment was performed using a three-layered structure composed of a Co layer, an NOL, and a Co layer as a fixed magnetic layer, it was found that, although the rate (ΔR/R) of change in resistance is increased as that of the three-layered structure composed of the CoFe layer, the NOL, and the CoFe layer, the unidirectional exchange bias magnetic field (Hex*) is considerably decreased. The unidirectional exchange bias magnetic field (Hex*) is the intensity of a magnetic field including an exchange coupling magnetic field generated between the fixed magnetic layer and an antiferromagnetic layer, a coupling magnetic field by the RKKY interaction generated between magnetic layers when the fixed magnetic layer has a synthetic ferrimagnetic pinned structure, and the like.
In addition, according to the experiments which will be described later, it was found that the rate (ΔR/R) of change in resistance and the unidirectional exchange bias magnetic field (Hex*) are considerably changed, particularly by the film thickness of a magnetic layer formed between the NOL and a nonmagnetic material layer made of Cu or the like, the shape of the NOL, and the like. Hence, the inventors of the present invention intended to optimize materials and film thicknesses of magnetic layers provided on the top and the bottom of the NOL and the shape thereof so that the rate (ΔR/R) of change in resistance and the unidirectional exchange bias magnetic field (Hex*) are further increased as compared to those obtained in the past, and as a result, the present invention was made.